In the iron and steel industry, it is necessary to treat the ferrous base metals while in the molten state with a desulfurizing agent to reduce the sulphur content of the metal product. Magnesium metal is a powerful deoxidizer and desulfurizer. However, magnesium metal boils at a low temperature and therefore, the sudden increase in volume which is produced when metallic magnesium is added to the molten iron, may result in violent reactions as the magnesium metal is vaporized.
Various methods have been used to reduce this violent activity by slowly introducing the magnesium metal into molten ferrous metal under rigidly controlled systems. One of these methods for reducing the violence is to impregnate porous bodies with magnesium metal and to introduce these magnesium impregnated porous bodies into the molten ferrous metal. Under these conditions, the impregnated magnesium metal is released at a slow enough rate that the violence is held to minimum.
Among the known porous bodies which have been used with limited success for this purpose are: porous coke, carbon, graphite and ceramic bodies such as quicklime, lump limestone or dolomite and the like.
In addition, magnesium has been infiltrated into porous iron bodies. Among these prior art iron bodies is sponge iron in which the iron particles are very small and are sintered together to form a porous structure. Sponge iron itself is expensive to produce and to use. The cost of forming large porous structures from sponge iron is also an expensive procedure.
Since the pores of the sponge iron are excessively small, they tend to release the magnesium too slowly when immersed into the molten iron, and the release may be too quiescent for optimum operation. Sponge iron also may contain oxides which may form a violent reaction with the magnesium which may also impair the efficiency.
Another method used by the prior art to produce iron briquettes containing magnesium is to dry-press together iron particiles and magnesium particles, both of which preferably are from 4-60 mesh.
When these compressed iron and magnesium particles are used to desulfurize molten iron, the remaining iron structure becomes decidedly weak as the magnesium melts and, therefore, the magnesium may be released too quickly and therefore may cause a violent reaction.
In contrast to these prior art products, the instant invention prepares a network of ferrous metal pieces, particularly steel turnings, compressed together which forms a body having a low density, high porosity, and high strength which may be infiltrated with large quantities of magnesium metal.
The voids in the metal network are sufficiently large to release the magnesium at a desirable rate, i.e., fast enough to provide rapid treatment, but not too fast so that the treatment is unduly violent.
It has been found that the porous ferrous metal netowrk of the instant invention possesses advantages which are not present in the prior art porous bodies.